1. Field of the Invention
The present invention relates to an idling stop device that sets a vehicle speed optimum for starting an idling stop based upon external environment recognized by an external environment recognition unit.
2. Description of Related Art
Conventionally, the idling stop device of this type stops an engine after an elapse of a predetermined time after a driver completely stops a vehicle (0 [Km/h]) in consideration of change of mind (in re-acceleration just before or just after a driver stops the vehicle).
However, there has recently been known a technique of determining an idling stop condition (determining whether or not a brake pedal is depressed, and a vehicle speed is not more than a vehicle speed of starting an idling stop (20 [Km/h])), and when this condition is satisfied, an engine is stopped before the vehicle completely stops, as described in Japanese Unexamined Patent Application Publication No. 2010-230160.
The technique described in this publication stops the engine before the vehicle stops, thereby enhancing fuel economy.
In the technique described in the above-mentioned publication, the vehicle speed for starting the idling stop is uniformly set. However, there may be the case in which it would be better not to stop the engine depending upon external environment, even when the idling stop condition described above is satisfied
For example, when a lighting color of a traffic light is changed from red to blue during deceleration before the vehicle stops, a driver depresses an accelerator pedal to again speed up the vehicle. If the idling stop condition is satisfied during the deceleration, the engine is uniformly stopped (idling stop), so that there is a delay in the re-acceleration, which might provide a feeling of strangeness to the driver.
When a line of cars waiting at stoplights is relatively long, a preceding vehicle does not start immediately even when the traffic light ahead is changed from red to blue, and therefore, the engine can be stopped (idling stop) relatively early.
As described above, the vehicle speed for starting the idling stop by the idling stop device is varied according to the external environment. In the technique described above, the idling stop condition is uniformly determined, so that the optimum idling stop timing cannot be obtained, resulting in that it is difficult to realize satisfactory fuel economy and drivability.